rename setPreferencesValue() into xmlSetValues()
@sgougeon)
Reported by Samuel GOUGEON (BUG DESCRIPTION:
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getPreferencesValue() has been cloned into xmlGetValues() and will be removed from Scilab 6.1.x (bug 15433).
The same should be done for setPreferencesValues(), to be renamed into xmlSetValues().
For the time being, unlike xmlGetValues(), only one value can be set with a call,
but this could be extended to several values later.